1. Field of the Invention
The present invention relates to a heat exchanger member, such as a heat absorber or heat rejector, provided in a Stirling cycle refrigerator, to a heat exchanger element for use in such a heat exchanger member, and to a method of manufacturing such a heat exchanger member.
2. Description of the Related Art
First, a typical configuration of a free-piston-type Stirling cycle refrigerator exploiting a Stirling cycle will be described. FIG. 29 is a diagram schematically showing a section, as seen from the side, of a free-piston-type Stirling cycle refrigerator. Inside a cylinder 1, a heat absorber 2 acting as a low-temperature portion, a regenerator 3, and a heat rejector 4 acting as a high-temperature portion are arranged in this order. The heat absorber 2 and the heat rejector 4 are each built as a heat exchanger member composed of a tubular body 21 or 41 having a heat exchanger element 22 or 42 fitted on the inner surface thereof at one end. Inside the cylinder 1, the heat exchanger elements 22 and 42 are each contiguous to the regenerator 3.
Inside the cylinder 1 are also arranged a displacer 6 firmly fitted to one end of a displacer rod 5, and a piston 7 through which the displacer rod 5 is placed. The other end of the displacer rod 5 is connected to a spring 8. Inside the cylinder 1, the displacer 6 and the piston 7 create an expansion space 9 in the heat absorber 2 and a compression space 10 in the heat rejector 4. The expansion space 9 and the compression space 10 communicate with each other through the regenerator 3, and thereby form a closed circuit.
Now, how this free-piston-type Stirling cycle refrigerator operates will be described. The piston 7 is made to reciprocate along the axis of the cylinder 1 with a predetermined period by an external power source, such as a linear motor (not shown). The compression space 10 is filled with working gas, such as helium, beforehand.
As the piston 7 moves, the working gas in the compression space 10 is compressed. This causes the working gas to flow through the heat exchanger element 42 then through the regenerator 3 into the expansion space 9 (as indicated by broken-line arrows A in the figure). Meanwhile, the working gas first releases heat in the heat rejector 4, by exchanging the heat produced therein as a result of compression with the air outside, and is then precooled as it passes through the regenerator 3, by receiving the cold accumulated in the regenerator 3 beforehand.
When the working gas flows into the expansion space 9, it presses the displacer 6 rightward against the spring 8. Thus, the working gas expands, and produces cold therein. When the working gas expands to a certain degree, the resilience of the spring 8 presses the displacer 6 back in the opposite direction.
As a result, the working gas in the expansion space 9 flows through the heat exchanger element 22 of the heat absorber 2 and then through the regenerator 3 back to the compression space 10 (as indicated by solid-line arrows A′). Meanwhile, the working gas first absorbs heat in the heat exchanger element 22, by exchanging heat with the air outside, and is then preheated as it passes through the regenerator 3, by receiving the heat accumulated in the regenerator 3 beforehand. The working gas back in the compression space 10 is then compressed again by the piston 7.
Through the repetition of this cycle of events, cryogenic cold is obtained in the heat absorber 2. Here, the larger the amount of heat absorbed in the heat exchanger element 22 of the heat absorber 2 and the amount of heat released in the heat exchanger element 42 of the heat rejector 4, the better. This helps increase the efficiency with which the regenerator 3 precools and preheats the working gas, and thus helps reduce the burden on the regenerator 3, leading to better chilling performance of the Stirling cycle refrigerator.
Next, the heat rejector 4 acting as the high-temperature-side heat exchanger member of the Stirling cycle refrigerator described above will be described with reference to FIG. 30. It is to be understood that, although the following description deals only with the heat rejector 4 and its heat exchanger element 42, the heat absorber 2 acting as the low-temperature-side heat exchanger member and its heat exchanger element 22 are configured in the same manner.
As FIG. 30 shows, this heat exchanger element 42 is built as an annular corrugate fin 421 produced by forming a corrugated sheet material into a cylindrical shape. Thus, the heat exchanger element 42 has a rugged surface, with a large number of axially-extending straight V-shaped grooves 421a formed at regular intervals.
Here, the portions of the heat exchanger element 42 which protrude toward the center of the body 41 of the heat rejector 4 are referred to as the bottoms 421b of the individual grooves 421a, and the portions of the heat exchanger element 42 which protrude toward the inner surface of the body 41 are referred to as the tops 421c between every two adjacent grooves 421a. The diameter of the circle formed by smoothly connecting all the tops 421c together (i.e. the external diameter of the annular corrugate fin 421) is substantially equal to the internal diameter of the body 41. The body 41 and the annular corrugate fin 421 are arranged so as to be coaxial with each other.
The inner surface of the body 41 and the tops 421c of the annular corrugate fin 421 are firmly fixed together with adhesive or solder. FIG. 31 is an enlarged view of a portion of the annular corrugate fin 421 as seen axially, and shows how it is fixed with adhesive. In this case, first, adhesive 11 is applied thinly to the inner surface of the body 41, and then the annular corrugate fin 421 is inserted into the body 41. Then, with the annular corrugate fin 421 held in the desired position for a while, the adhesive 11 is dried.
On the other hand, FIG. 32 shows how the annular corrugate fin 421 is fixed with solder. In this case, first, the annular corrugate fin 421 is inserted into the body 41. Then, with the annular corrugate fin 421 held in the desired position, solder 12 is applied to where the inner surface of the body 41 makes contact with or comes close to the tops 421c of the annular corrugate fin 421.
However, with this conventional heat exchanger member described above, the fixing together of its components with adhesive or solder is performed by hand. Thus, this process takes too much trouble and time, hindering the improvement of productivity and the reduction of manufacturing costs. Moreover, the heat exchanger member thus manufactured is prone to variations in quality, specifically in heat exchange performance, and thus tends to lack in stability and reliability.
Furthermore, as the Stirling cycle refrigerator is used for an extended period, if the annular corrugate fin 421 is damaged, it is impossible to simply remove and replace it. This adds to the economic burden on the user in the event of repair, and is contrary to the general trend toward recycling of resources in view of the global environment.